JP6443955B2 - Semiconductor laser device - Google Patents

Description

  The present invention relates to a semiconductor laser light source, and more particularly to a semiconductor laser light source and a semiconductor laser device that operate in a single mode used in optical sensing of medium and long distance optical fibers and gas.

  In recent years, with the increase in capacity of optical communication systems, digital coherent communication systems using multi-level phase amplitude modulation have begun to spread. Since this communication method is a method for transmitting a digital signal using phase information of light, a light source for supplying carrier light requires a laser light source with little phase noise and a narrow spectral line width.

  There are various types of laser light sources, but semiconductor lasers are widely used as light sources for optical communication because of their small size and low cost. In particular, in medium and long distance optical communication systems, distributed feedback (DFB) lasers that operate in a single mode are widely used. Also, in a medium / long-distance optical communication system, wavelength division multiplexing (WDM) technology is generally used in order to increase the transmission capacity per optical fiber. Therefore, a wavelength variable characteristic capable of outputting an arbitrary wavelength channel is also required for a light source for digital coherent communication.

  Since the semiconductor laser has a smaller resonator size than other solid-state lasers and gas lasers, the phase noise is relatively large. For example, the line width of an ordinary semiconductor laser having a resonator size of several hundred μm is in the order of MHz. Here, the line width means a spectral line width, and is represented by a full width at half maximum (FWHM) of the spectrum. In a 100 Gbit / s digital coherent communication system that is currently in widespread use, a polarization multiple quadrature phase shift keying (QPSK) modulation method is used, and a laser light source has a frequency of several hundred kHz. Spectral line width is required. For such applications, a tunable DFB laser array, an external resonator type laser, or the like in which the resonator length is increased to about 1 mm to narrow the spectrum is used. Realization of a light source with a narrower spectral line width is expected in the future in order to realize a larger-capacity communication by using a modulation scheme having a higher multilevel. Also, in optical sensing applications other than communication, in order to observe a narrow absorption line spectrum with high sensitivity, it is required to narrow the spectrum of the light source.

M. Finot, et al., “Thermally tuned external cavity laser with micromachined silicon etalons: design, process and reliability,” Electronic Components and Technology Conference 2004 Proceedings, Vol.1, pp.818-823, 2004 K. Petermann, “External optical feedback phenomena in semiconductor lasers,” IEEE J. Quantum Electron., Vol.1, No.2, pp.480-489, 1995

  As a semiconductor laser capable of narrowing the spectral line width to about 10 kHz, there is a so-called external resonator type laser in which an optical resonator is formed outside a semiconductor chip. For example, Non-Patent Document 1 discloses an external resonator type laser including a semiconductor optical amplifier, an external reflector, an etalon filter for selecting a wavelength, and a lens. It has been reported that with this configuration, a wavelength variable characteristic covering the entire C band of 1550 nm and a line width characteristic of several tens of kHz were obtained. However, the external resonator type laser requires a large number of parts in addition to the semiconductor chip, and further, it is necessary to assemble these with high accuracy. Further, in the external resonator type laser, in order to select one wavelength from a large number of resonance modes, at least two wavelength filters must be controlled, and there is a problem that the control circuit becomes complicated. It was. Further, in the manufacturing process of the semiconductor laser device, there has been a problem that the wavelength characteristic test / inspection becomes complicated.

  As another configuration for narrowing the spectral line width, a tunable laser based on a DFB laser is also known. In this configuration, the wavelength can be changed using temperature control or the like while maintaining the same oscillation mode in principle. For this reason, the control for changing the wavelength becomes simple. By increasing the resonator length to about 1 mm, the DFB laser-based wavelength tunable laser has a line width of up to about 100 kHz. However, if the resonator is further lengthened, it becomes difficult to maintain the uniformity of the pitch of the diffraction grating and the uniformity of the equivalent refractive index of the optical waveguide constituting the resonator. Therefore, with a long resonator, it becomes difficult to form a uniform resonator due to manufacturing fluctuations, and even with a DFB laser-based tunable laser, there is a limit to narrowing the spectral linewidth.

  It is known that the effect of narrowing the spectral linewidth can be obtained by feeding back part of the oscillation light of the semiconductor laser from the outside. For example, Non-Patent Document 2 shows a configuration in which light is fed back to a semiconductor laser using an optical fiber. According to the configuration of Non-Patent Document 2, the spectral line width can be narrowed by two orders of magnitude or more by returning a part of the light from the outside to the semiconductor laser. However, the method using an optical fiber has a difficulty in oscillation stability. The oscillation state of the semiconductor laser is sensitive to the phase of the feedback light, and when the phase state of the feedback light changes, a wavelength jump due to the external resonance mode occurs. In other words, in the feedback type configuration using an optical fiber, the oscillation state becomes unstable with respect to minute changes such as displacement, stress, temperature, etc. of the optical fiber. It was difficult to use.

  The present invention has been made in view of such a problem, and an object of the present invention is to realize a light source that is composed of a semiconductor laser, is small in size, has good controllability, and has a narrowed spectrum. is there.

  According to one embodiment of the present invention, a first substrate on which a semiconductor laser that oscillates in a single mode is formed, and after a part of output light from the semiconductor laser propagates a certain optical path length, the semiconductor laser A second substrate on which a lightwave circuit configured to return to the substrate is formed, and the first substrate and a third substrate on which the second substrate is mounted, and the semiconductor of the first substrate The semiconductor laser device is characterized in that the output light from the laser is optically coupled to the input waveguide of the light wave circuit of the second substrate.

  Preferably, the lightwave circuit on the second substrate includes a reflector that reflects the propagated light, and the light reflected by the reflector is configured to return to the semiconductor laser. Can do.

  The lightwave circuit on the second substrate may include branching means for branching the output light from the semiconductor laser to generate the part of the output light. Further, the first substrate branches the output light from the semiconductor laser into two, generates the part of the output light of the second substrate as one branched light, and the other branch A first semiconductor optical amplifier that amplifies the one branched light of the branching means, and amplifies the other branched light of the branching means; A second semiconductor optical amplifier can also be included.

  Preferably, the output light from the semiconductor laser on the first substrate and the input waveguide of the light wave circuit on the second substrate face the end surface of the first substrate and the end surface. There may be a bond between the end faces of the second substrate.

  The semiconductor laser may be a distributed feedback (DFB) laser or a distributed reflection (DBR) laser having a wavelength selection function using a diffraction grating. Preferably, the semiconductor laser includes N distributed feedback (DFB) laser arrays, an optical multiplexer configured to multiplex output lights from the N DFB laser arrays, and a semiconductor optical amplifier. And can operate as a wavelength tunable laser. The semiconductor laser is integrated with N distributed reflection (DBR) laser arrays, an optical multiplexer configured to multiplex output lights from the N DBR laser arrays, and a semiconductor optical amplifier. It can also operate as a wavelength tunable laser. The above-described optical multiplexer can be configured as an N-to-1 optical multiplexer, or can be configured as an N-to-2 optical multiplexer / demultiplexer.

  According to the present invention, a part of the output light of the semiconductor laser is returned to the semiconductor laser by using a light wave circuit for optical feedback, thereby enabling an operation with a narrowed spectrum. It is composed of a combination of a semiconductor laser chip and a lightwave circuit chip, and realizes a light source having a small size, good controllability, and a narrowed spectrum.

FIG. 1 is a diagram schematically illustrating a semiconductor laser device according to a first embodiment of the present invention. FIG. 2A is a top view showing a more detailed structure of the wavelength tunable semiconductor laser chip of the semiconductor laser device of the present invention. FIG. 2B is a cross-sectional view of the wavelength tunable semiconductor laser chip of the semiconductor laser device of the present invention along the oscillator length direction. FIG. 2C is a cross-sectional view perpendicular to the oscillator length direction of the wavelength tunable semiconductor laser chip of the semiconductor laser device of the present invention. FIG. 3 is a diagram showing a more detailed structure of the lightwave circuit chip of the semiconductor laser device of the present invention. FIG. 4 is a diagram for explaining the spectral line width characteristics of the semiconductor laser device of the present invention. FIG. 5 is a diagram schematically illustrating a semiconductor laser device according to the second embodiment of the present invention. FIG. 6 is a diagram schematically showing a semiconductor laser device according to the third embodiment of the present invention.

  In the semiconductor laser light source of the present invention, an operation with a narrowed line width can be performed by returning a part of the output light of the semiconductor laser to the semiconductor laser using a light wave circuit for optical feedback. As described above, in the configuration in which light is fed back to the semiconductor laser using the optical fiber in Non-Patent Document 2, the oscillation state becomes unstable with respect to minute changes such as displacement, stress, and temperature of the optical fiber, It was difficult to use in an actual communication device environment.

  On the other hand, in the semiconductor laser device of the present invention, a lightwave circuit for optical feedback is constituted by an optical waveguide that is not deformed, and the substrate including the lightwave circuit is the same substrate as the substrate on which the semiconductor laser is held. Arranged above. For this reason, it is possible to ensure the stability of the operating environment of the optical feedback circuit. Further, in the optical feedback configuration of the semiconductor laser device of the present invention, the function of the wavelength selection filter is not included in the light wave circuit, and the wavelength variable function of the semiconductor laser is used. For this reason, there is an advantage that it is not necessary to precisely adjust the wavelength of the filter as in the configuration of the external cavity laser. As described above, in the configuration of the semiconductor laser device of the present invention, it is possible to realize a light source that is small and stable, has good wavelength controllability, and has a narrow spectral line width. In the following description, the semiconductor laser light source and the semiconductor laser device are used as having the same meaning. Various embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram schematically illustrating a semiconductor laser device according to a first embodiment of the present invention. The semiconductor laser device 100 of this embodiment includes a wavelength tunable semiconductor laser chip 102 and a lightwave circuit chip 103 for optical feedback mounted on a single substrate 101. Lenses 104 and 105 are arranged on the output end side of the wavelength tunable semiconductor laser chip 102 so that the output light enters the input waveguide of the lightwave circuit chip 103. As the material of the substrate 101, a metal material such as tungsten copper alloy (CuW) having good thermal conductivity is used. Although not depicted in FIG. 1, a TEC (Thermo-Electric Cooler) is disposed on the back surface of the substrate 101, and the temperature of the entire substrate 101 can be controlled.

  The output light from the wavelength tunable semiconductor laser chip 102 is first converted into a collimated beam by the lens 104 and then condensed by the lens 105 onto the input waveguide of the lightwave circuit chip. As will be described later, a part of the optical output of the wavelength tunable semiconductor laser chip 102 is reflected from the light wave circuit 103 and returned. This reflected light follows an optical path opposite to the outgoing path to the light wave circuit 103 and is fed back to the output waveguide of the wavelength tunable semiconductor laser chip. In the light wave circuit 103, light other than the feedback light is guided to the output waveguide as output light. The output light from the light wave circuit 103 is converted into a collimated beam by the lens 106 and is used as the output light of the semiconductor laser device through the optical isolator 107. The optical isolator 107 is used to prevent laser oscillation from becoming unstable due to return light from the outside of the semiconductor laser device. When it is desired to guide light to the optical fiber, the collimated beam after passing through the isolator may be input to the optical fiber using a condenser lens.

  2A to 2C are diagrams showing a more detailed structure of the wavelength tunable semiconductor laser chip in the semiconductor laser device of the present invention. FIG. 2A is a top view of the wavelength tunable semiconductor laser chip 102 as seen from the substrate surface. 2B is a cross-sectional view taken along line IIB-IIB in the top view of FIG. 2A and perpendicular to the substrate surface along the length direction of the resonator. 2C is a cross-sectional view taken along line IIC-IIC in the top view of FIG. 2A perpendicular to the substrate surface and perpendicular to the length direction of the resonator. The wavelength tunable semiconductor laser chip of FIG. 2A has a DFB laser array type configuration in which each of four DFB lasers 201a to 201d, an optical multiplexer 203, and a semiconductor optical amplifier 204 are integrated on an InP substrate. Each portion is connected by waveguides 202a and 202b. Referring to the cross-sectional view along the laser resonator of FIG. 2B, in one DFB laser, a guide layer 213 having a diffraction grating 214 formed on an active layer 212 having an amplifying action by injecting a current is provided. Prepare. These layers 212, 213, and 214 are further sandwiched between the n-type InP clad layer 216 and the p-type InP clad layer 217.

  The laser oscillation operation occurs by grounding the n-side electrode 219, applying a positive voltage to the p-side electrode 220, and injecting a current into the active layer 212. At this time, since only the wavelength determined by the period of the diffraction grating 214 is strongly fed back, single mode oscillation occurs near this wavelength. As shown in the cross-sectional view of the laser resonator in FIG. 2C, a single DFB laser has a so-called embedded waveguide structure in which the active layer 212 and the guide layer 213 are embedded with InP. Have. The n-type InP current blocking layer 221 is provided to efficiently inject current into the active layer 212.

  The optical multiplexer 203 is composed of a multi-mode interference type waveguide with 4 inputs and 1 output. The waveguide transparent core layer 215 (corresponding to the waveguide 202a in FIG. 2A) formed continuously from the DFB laser is formed of an InGaAsP mixed crystal having a composition transparent to the oscillation light. The semiconductor optical amplifier 204 is configured by a waveguide 212 having a gain similar to each of the DFB lasers 201a to 201d. However, the diffraction grating 214 is not formed, and a so-called SOA (Semiconductor Optical Amplifier) is configured. Yes. The specific structure, material, and configuration parameters of each part of the DFB laser described above are exemplary, and can be used as a laser light source applicable to a digital coherent communication system using multilevel phase amplitude modulation. The semiconductor laser is not limited to the specific example described above.

  In the wavelength tunable semiconductor laser chip 102, in order to prevent the light emitted from the waveguide in the chip from being reflected by the chip end face, the waveguide is formed so as to be slightly inclined rather than perpendicular to the chip end face. . Furthermore, antireflection films 211a and 211b are formed on the end face of the chip. By controlling the amount of current flowing through the semiconductor optical amplifier 204, the light output level can be adjusted. Since the diffraction gratings formed in the DFB lasers 201a to 201d of the DFB laser array are formed at different pitches, each operates so as to oscillate at a different wavelength corresponding thereto. It is possible to change the wavelength of the output light by selecting one DFB laser that oscillates by passing a current from the DFB laser array. In this embodiment, in the 1550 nm band, the oscillation wavelength of each DFB laser array is set so as to have a wavelength interval of about 4 nm at a predetermined temperature. The oscillation wavelength of the DFB laser changes by about 0.1 nm on the long wavelength side when the chip temperature changes once. Therefore, if the laser temperature is changed by 40 degrees in the range of 20 ° C. to 60 ° C., the oscillation wavelength can be changed by 4 nm. The wavelength can be continuously changed to an arbitrary wavelength between the oscillation wavelengths of the four DFB lasers 201a to 201d at a predetermined temperature. In the case of the configuration of this embodiment shown in FIGS. 2A to 2C, it is possible to oscillate at an arbitrary wavelength in a wavelength range of 4 × 4 nm = 16 nm. 2A to 2C exemplarily show an array configuration including four DFB lasers. However, if the number of DFB laser arrays is increased, the wavelength variable range can be further expanded according to the number of arrays.

FIG. 3 is a diagram showing a more detailed structure of the lightwave circuit chip of the semiconductor laser device of the present invention. The lightwave circuit 103 is produced by depositing a SiO ₂ glass film on a Si substrate. The optical waveguide 301 has a structure in which a rectangular core layer having a high refractive index is embedded with a cladding layer having a low refractive index. In this example, the refractive index difference between the core layer and the cladding layer was about 2.5%. The oscillation light from the wavelength tunable semiconductor laser chip 102 shown in FIG. 2A enters the light input portion 302 of the optical waveguide 301 through the lenses 104 and 105. Incident light propagates through the optical waveguide 301, and is divided into light propagating to the light output unit 303 and light propagating to the light reflector 305 by the directional coupler 306. The waveguide that guides part of the oscillation light to the light reflector 305 is set so that its optical path length is increased to a certain extent. The spectral line width is known to narrow in inverse proportion to the square of the optical path length, and the narrowing effect of the spectral line width is higher when the optical path length from the laser output unit to the light reflector 305 is increased to a certain extent. It is. In order to make the spectral line width 10 kHz or less, 10 cm or more is necessary, and 40 to 50 cm or less is preferable for stable operation. In the optical waveguide 301 of this example, the optical path length from the light input unit 302 to the light reflector 305 was set to about 13 cm. The light reflected by the reflector 305 propagates in the opposite direction through the optical waveguide, returns to the optical input unit 302, and finally returns to the semiconductor laser chip 103. A part of the reflected light propagates to the optical monitor output unit 304 by the directional coupler 306.

  In the optical input unit 302, the optical output unit 303, and the optical monitor output unit 304 of the lightwave circuit 103, the propagation direction of the optical waveguide is inclined with respect to the end surface of the chip so as not to reflect light at the end surface of the chip. Configured. In particular, in the light input portion 302 and the light output portion 303, antireflection AR films 307a and 307b are respectively formed on the end faces in order to keep light reflection low. On the other hand, in the light reflector 305, in order to obtain constant light reflection, the optical waveguide is configured to be perpendicular to the chip end face, and the surface of the reflector 305 is coated with a highly reflective film 308. Yes.

  In the configuration example of the lightwave circuit chip in FIG. 3, an example in which the reflector 305 is provided at one end of the chip to obtain reflected light is shown, but the configuration is not necessarily limited to this configuration. For example, a loop type reflector configured by combining a splitter and a waveguide may be formed on a light wave circuit, and the oscillation light from the wavelength tunable semiconductor laser chip 102 may be reflected by the loop type reflector.

  Therefore, the semiconductor laser device of the present invention propagates a part of the output light from the first substrate 102 on which the semiconductor lasers 201a to 201d oscillating in a single mode are formed and a certain optical path length. A second substrate 103 on which a lightwave circuit configured to return to the semiconductor laser is formed, and a third substrate 101 on which the first substrate and the second substrate are mounted. The semiconductor laser device is characterized in that the output light from the semiconductor laser on the first substrate and the input waveguide of the light wave circuit on the second substrate are optically coupled.

  Preferably, the light wave circuit includes a reflector 305 that reflects the branched light, and the light reflected by the reflector can be configured to return to the semiconductor laser. More preferably, the lightwave circuit on the second substrate may include a branching unit 306 that branches the output light from the semiconductor laser to generate the part of the output light.

  FIG. 4 is a diagram for explaining the spectral line width characteristics of the semiconductor laser device of the present embodiment. FIG. 4 shows changes in the spectral line width when a current of 150 mA is injected into one laser in the DFB laser array and the current value flowing through the semiconductor optical amplifier (SOA) 204 is changed. At this time, the temperature of the semiconductor laser device 100 was controlled to be 25 ° C. The spectral line width was measured by the delayed self-heterodyne method. When the SOA current is low, the spectral line width is thick because the amount of optical feedback to the DFB laser is small, but when the SOA current value is increased to about 60 mA, the spectral line width is narrowed to 10 kHz or less. The spectral line width of the single DFB laser array was about 2 to 3 MHz. It was confirmed that the spectral line width was narrowed by two orders of magnitude or more with respect to the DFB laser array alone by the configuration of the semiconductor laser device of the present invention including the light wave circuit for optical feedback. As shown in FIG. 4, when the SOA current value was 180 mA or more, the oscillation mode became unstable due to too much optical feedback, and the spectral line width rather increased. Therefore, in the case of the configuration of this embodiment, if the SOA current value is used at around 100 mA, an oscillation operation in which the spectral line width is stably narrowed becomes possible.

  In this embodiment, the DFB structure in which a diffraction grating is formed on a waveguide having a gain has been described as an example of the structure of the semiconductor laser. However, a DBR (Distributed) in which the diffraction grating is formed in a waveguide having no gain is described. A Bragg Reflector type structure may be used. In addition, the present invention can be applied to a single DFB laser or DBR laser instead of a laser array including a plurality of DFB lasers as shown in FIGS. 2A to 2C. Further, the waveguide structure constituting the laser has been described by taking the buried type as shown in FIG. 2C, but the present invention is also applicable to a laser having a waveguide having a ridge structure. In the semiconductor laser device of the present invention, a lightwave circuit for optical feedback is configured by an optical waveguide that is not deformed, and is disposed on the same (common) substrate as the substrate on which the semiconductor laser is configured. The stability of the circuit operating environment can be ensured. Therefore, if the optical feedback circuit is configured on a single substrate, the configuration of the feedback circuit is not limited to that shown in FIG.

  In the configuration of the semiconductor laser device of the present invention shown in FIG. 1, the semiconductor laser chip 102 integrated on the InP substrate is described as being directly mounted on the common substrate 101. However, if the two substrates are firmly fixed, the effect of the present invention can be obtained in the same manner. Therefore, the fixing between the two substrates 101 and 102 may be performed by any method. Further, although the semiconductor laser chip 102 is shown as one substrate in FIG. 1, the chip including the semiconductor laser and other optical components / electrical components are mounted on one other substrate, and the other substrate is mounted on the common substrate 101. May be installed.

  Similarly, the light wave circuit chip 103 may be fixed between the two substrates 101 and 103 by any method, and may be directly fixed or fixed with some base material interposed therebetween. Further, a chip including a light wave circuit and other optical components may be mounted on one different substrate, and the other substrate may be mounted on the common substrate 101.

  In the configuration of the semiconductor laser device of this embodiment, the optical circuit for optical feedback is configured by an optical waveguide that is not deformed, and is disposed on the same substrate as the substrate on which the semiconductor laser is held. This makes it possible to ensure the stability of the operating environment of the optical feedback circuit. In the optical feedback configuration of the semiconductor laser device of the present invention, the wavelength selection function of the semiconductor laser is used instead of the wavelength selection filter function in the light wave circuit. For this reason, it is not necessary to precisely adjust the wavelength of the filter as in the configuration of the external cavity laser. A light source that is configured by a combination of a semiconductor laser chip and a lightwave circuit chip, is small in size, has good wavelength controllability, and has a narrow spectral line width.

  FIG. 5 is a diagram schematically illustrating a semiconductor laser device according to the second embodiment of the present invention. Compared to the semiconductor laser device of the first embodiment, the semiconductor laser chip 102 and the lightwave circuit chip 103 are disposed so as to be in contact with each other, and the output light from the semiconductor laser chip 102 is directly coupled to the light input portion of the lightwave circuit chip 103. It is different in that. Other configurations are the same as those in the first embodiment. In order to keep the optical coupling efficiency high, the light spot size at the light output portion of the semiconductor laser chip 102 and the light spot size at the light input portion of the lightwave circuit chip 103 are as close as possible to each other in the vicinity of the chip end. The waveguide is optimally configured. For example, the angle of inclination of the waveguide at the end of each chip is set so that the chip end faces can be directly coupled without a decrease in optical coupling efficiency.

  Therefore, in the semiconductor laser device of this embodiment, the output light of the semiconductor laser on the first substrate 102 and the input waveguide 301 of the lightwave circuit on the second substrate 103 are opposed to each other on the first substrate. The present invention can be carried out by combining the end face and the end face of the second substrate. In the configuration of this embodiment, it is necessary to mount the semiconductor laser chip 102 and the lightwave circuit chip 103 on the substrate 101 with submicron accuracy. However, since the optical coupling between the chips is directly performed without using the two lenses 104 and 105 provided in the first embodiment, an area for mounting the lens becomes unnecessary, and the semiconductor laser device is further improved. Miniaturization is possible.

  Also in the semiconductor laser device of the present embodiment, as in the first embodiment, by injecting an appropriate current value into the SOA, the spectral line width is narrowed by about two to three orders of magnitude compared to the case of the semiconductor laser alone. It becomes possible. Even in the configuration of the semiconductor laser device of the present embodiment, the optical circuit for optical feedback is configured by an optical waveguide that is not deformed, and is disposed on the same substrate as the substrate on which the semiconductor laser is configured and held. . Thereby, the stability of the operating environment of the optical feedback circuit can be ensured.

  If the SOA chip is further integrated between the lightwave circuit chip 103 and the lens 106, it is possible to amplify the light by the SOA and further increase the light output level.

  In the semiconductor laser devices of the first and second embodiments described above, both the oscillation light of the semiconductor laser chip and the feedback light from the lightwave circuit chip propagate through the common semiconductor optical amplifier (SOA) 204. Further, as described with reference to FIG. 4, the spectral line width is controlled by changing the SOA current. In such a configuration, when the SOA current is determined for the spectral line width, the output level of the oscillation light also changes at the same time, so it is difficult to arbitrarily set the optical output level from the semiconductor laser device. Therefore, in this embodiment, another configuration example is presented in which the optical output level and the spectral line width can be independently controlled while maintaining the effects of the present invention.

  FIG. 6 is a diagram schematically showing a semiconductor laser device according to the third embodiment of the present invention. The semiconductor laser device 500 of the present embodiment also has an embodiment in that the semiconductor laser chip 502 and the lightwave circuit chip 510 are formed on a single substrate 501, and the two chips are directly optically coupled without a lens. It is similar to the configuration of 2. However, it differs from the configuration of the second embodiment in that the combined output of the oscillation light from the semiconductor laser chip is divided into two, the oscillation light output route and the feedback light route.

  Specifically, the semiconductor laser chip 502 of the present embodiment uses, for example, a 4-input 2-output optical multiplexer / demultiplexer 503 as an optical multiplexer that multiplexes oscillation light from four DFB lasers 506a to 506d. The multiplexer / demultiplexer 503 outputs the output light from the four DFB lasers via the first SOA 508 to the outside as the output light of the semiconductor laser device, and the second SOA 507. Branches to the second route to be output to the lightwave circuit chip 510. As described above, the present embodiment is different from the configuration of the second embodiment in that the output light is branched into two routes by the optical multiplexer / demultiplexer 503 and a separate SOA is provided for each route. The optical multiplexer / demultiplexer 503 can be realized by a star coupler, a multimode interference optical multiplexer or the like. The lightwave circuit chip 510 includes a light reflector 511, an AR film 509, and an optical waveguide 512 having a predetermined length, and has the same configuration as that of the first and second embodiments.

  Therefore, the present invention provides a first substrate 502 on which a semiconductor laser that oscillates in a single mode is formed, and a part of output light from the semiconductor laser is propagated through a certain optical path length before the semiconductor laser. A second substrate 510 on which a lightwave circuit configured to return to the second substrate 510 and a third substrate 501 on which the first substrate and the second substrate are mounted are provided. A semiconductor laser device in which an output light from the semiconductor laser and an input waveguide of the light wave circuit of the second substrate are optically coupled, wherein the first substrate is supplied from the semiconductor laser. Branch means for branching the output light into two, generating the part of the output light of the second substrate as one branched light, and generating the output light of the semiconductor laser device as the other branched light 503 of the branching means Serial and first semiconductor optical amplifier 508 for amplifying one of the branched light, as having a second semiconductor optical amplifier 507 for amplifying the other branched light of said branch means, can be implemented.

  In the third embodiment shown in FIG. 6, since four DFB lasers are configured, a 4-input 2-output optical multiplexer / demultiplexer is used as the optical multiplexer / demultiplexer 503. However, the present invention is not limited to this configuration. . That is, an N-input 2-output optical multiplexer / demultiplexer can be provided according to the number N of DFB lasers. Further, a three-output optical multiplexer / demultiplexer may be used for monitoring the optical output level. With the configuration of the present embodiment, the current flowing through the first SOA 508 for optical output is independently controlled while the current flowing through the second SOA 507 for optical feedback is set to an optimum value that reduces the speckle line width. The light output level can be freely set. When there is a branch circuit (directional coupler) on the lightwave circuit chip side as in the first and second embodiments, a part of the output of the SOA 204 is branched by the directional coupler 306 in the output light of the semiconductor laser device. Since it is an output, the optical output level is always smaller than the output of the SOA 204. In the configuration of this embodiment, the output of the SOA 508 can be used as it is as the light output of the light source. As a communication light source, the ability to arbitrarily set the light output level is a great advantage. If the light output level as a light source is fixed, the application range is narrowed. By adopting a configuration in which the combined output is branched into two routes as in this embodiment, a light source capable of flexibly setting the spectral line width and the light output level can be realized. As described in the second embodiment, the light output level can be adjusted by further integrating the SOA chip between the lightwave circuit chip 103 and the lens 106. However, in this case, three chips are required for the entire semiconductor laser device, which causes an increase in member costs and assembly costs. Therefore, the output light from the semiconductor laser is divided into two routes, an oscillation light output route and a feedback light route. The divided configuration of this embodiment is superior.

  As described above in detail, according to the semiconductor laser device of the present invention, a part of the output light of the semiconductor laser is returned to the semiconductor laser by using the optical circuit for optical feedback. It becomes possible. A light source having a combination of a semiconductor laser chip and a lightwave circuit chip, a small size, good controllability, and a narrow linewidth in the spectrum can be realized.

  The present invention is generally applicable to an optical communication system. In particular, it can be used for a transmitter of an optical communication system. It can also be used for optical sensing systems.

Claims (8)

A first substrate on which a semiconductor laser that oscillates in a single mode is formed;
A second substrate made of Si on which a lightwave circuit configured to return a part of the output light from the semiconductor laser to the semiconductor laser after propagating a part of the optical path length;
A third substrate on which the first substrate and the second substrate are mounted,
An output light from the semiconductor laser on the first substrate and an input waveguide of the light wave circuit on the second substrate are optically coupled to each other.   The lightwave circuit on the second substrate includes a reflector that reflects the propagated light, and the light reflected by the reflector is configured to return to the semiconductor laser. The semiconductor laser device according to claim 1.   3. The light wave circuit on the second substrate includes branching means for branching the output light from the semiconductor laser to generate the part of the output light. Semiconductor laser device. The first substrate splits the output light from the semiconductor laser into two, generates the part of the output light of the second substrate as one branched light, and as the other branched light Branching means for generating output light of the semiconductor laser device,
The first semiconductor optical amplifier that amplifies the one branched light of the branching means, and the second semiconductor optical amplifier that amplifies the other branched light of the branching means. 2. The semiconductor laser device according to 2.   The output light from the semiconductor laser on the first substrate and the input waveguide of the lightwave circuit on the second substrate are opposed to the end surface of the first substrate and the end surface. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is coupled between end faces of the substrate.   6. The semiconductor laser device according to claim 1, wherein the semiconductor laser is a distributed feedback (DFB) laser or a distributed reflection (DBR) laser having a wavelength selection function by a diffraction grating.   The semiconductor laser includes N distributed feedback (DFB) laser arrays, an optical multiplexer configured to multiplex output lights from the N DFB laser arrays, and a semiconductor optical amplifier. 7. The semiconductor laser device according to claim 1, wherein the semiconductor laser device operates as a laser.   The semiconductor laser is composed of N distributed reflection (DBR) laser arrays, an optical multiplexer configured to multiplex output lights from the N DBR laser arrays, and a semiconductor optical amplifier. 7. The semiconductor laser device according to claim 1, wherein the semiconductor laser device operates as a laser.

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